1. Field of the Invention
The invention relates to an apparatus for manufacturing a multi-layered wiring board, and more particularly to an apparatus for manufacturing a multi-layered wiring board having interlayer connection made by conductive pillars. The invention also relates to an apparatus for manufacturing a multi-layered wiring board having conductive pillars formed on a conductive foil and an apparatus for manufacturing a multi-layered wiring board having a conductive foil having conductive pillars laminated with an insulating resin layer.
2. Description of the Related Arts
Demands for high-density mounting of electronic elements are increasing as various types of electronic equipment are made compact and highly advanced in performance. In response to such demands, a type of wiring board, such as printed wiring board being used extensively is a multi-layered wiring board which has a laminated structure with insulating layers and wiring layers alternately overlaid. The multi-layered wiring board has wiring layers overlaid into a multi-layered structure in order to respond to the demands for high density and high performance. Interlayer connection of a plurality of wiring layers has been established by PTH (pated through hole(s)).
The multi-layered wiring board with via holes such as PTHs for interlayer connection of wiring layers has a disadvantage that it is not easy to comply with the demands for high-density mounting.
For example, wiring or mounting of electronic elements cannot be made in an area where a through hole is formed. Therefore, improvement of wiring density and high-density mounting is limited. In these years, wiring of the printed wiring board is also made to have high density as electronic elements are mounted in high density. When through holes are made to have a small diameter to comply with fine patterning of wiring, there is a problem that reliable interlayer connection is hardly assured.
In addition, for the interlayer connection with through holes, a through hole forming step and a plating step are involved, making the manufacturing process lengthy, and it is also disadvantageous in view of productivity.
For example, a step for forming through holes requires to make holes one by one by drilling and takes a long time. Especially, when through holes are drilled so to have a smaller diameter in this step, productivity is extremely lowered. Besides, after forming the through holes, a polishing step for removing burrs and a plating step are required.
Furthermore, positions where through holes are formed are required to be determined with high precision. It is also necessary to consider adhesion of plating to the inner walls of the through holes. Therefore, accuracy and conditions to form the through holes are complex to control, and productivity is decreased.
Especially, when the through hole has a diameter of about 0.2 mm or below, its formation takes a long time, and productivity is heavily decreased. Such problems can be remedied when a multi-layered wiring board is formed by making interlayer connection by means of conductive pillars to be described afterward.
In addition, a plating step, that electrical connection among a plurality of wiring layers is made with through holes, has to make a complex control to adjust a density of chemicals and a temperature. Besides, an apparatus for forming through holes and a facility for plating constitute a heavy burden in view of costs.
As described above, when the interlayer connection is made for the multi-layered wiring board using the through holes, productivity of the wiring substrate such as a printed wiring board (PWB) is decreased. Therefore, such a multi-layered wiring board is hard to comply with a demand for low cost.
To simplify the electrical connection among the wiring layers of the multi-layered wiring board, there is also proposed a method to connect the wiring layers with the conductive pillars. This method forms conductive pillars, such as via lands, as interlayer connections formed on a wiring circuit, and inserts the conductive pillars into the interlayer insulating layer such as a prepreg in its thickness direction to connect with the via lands formed on the opposed wiring layer.
The interlayer connection of the wiring circuit using the conductive pillars has advantages that a structure is simple, steps are not many, productivity is high, and high-density mounting can be made. However, a printed wiring board having the interlayer connection of wiring circuits using the conductive pillars has disadvantages to be described as follows.
The conductive pillars are formed on a conductive foil such as a copper foil by screen printing a plurality of times using a mask. However, no apparatus was available to print those pillars automatically. In making multiple printings by the manpower, it is difficult to keep a fixed time interval between respective printing steps, and the conductive pillars formed do not have uniform quality. Additionally an aspect ratio of the conductive pillars can be adjusted by the number of printing times, but management of the number of times to print on very many conductive foils becomes a very large burden decrease a productivity.
FIG. 19A and FIG. 19B are diagrams schematically showing a step of producing a multi-layered wiring board using conventional conductive pillars, wherein an insulating resin layer is pierced by the conductive pillars which are formed on a conductive foil.
It is seen that a conductive foil 52 such as a copper foil having conductive pillars 51 having a substantially conical shape is laminated with an insulating resin layer 53 such as a prepreg in a semi-cured state (B-stage), then heated and pressed by a plane press to pierce the insulating resin layer 53 by the conductive pillars 51. Reference numerals 91a, 91b, denote press plates of the plane press. To keep the shape of the conductive pillars 51, a releasing sheet 56 is placed on the insulating resin layer 53.
However, the plane press is hard to press uniformly the entire area of the laminate. Therefore, all the conductive pillars 51 formed on the conductive foil 52 cannot pierce the insulating resin layer 53 satisfactorily due to non-uniform pressing. The conductive pillars 51 serve to make interconnection of the wiring layers of the multi-layered wiring board, so that such defective piercing is directly related to a failure of the multi-layered wiring board.
To pierce the conductive pillars 51 by the plane press, it is necessary to laminate the conductive foil 52, the insulating resin layer 53 and the releasing sheet 56 in each pressing process. After pressing, the laminate must be decomposed. Especially, when pressing is made manually, a long time is required to complete the process. Therefore, productivity of a wiring substrate is decreased.
Because of the drawbacks in the multi-layered wiring board having the interlayer connection made by the conductive pillars, it is hard to put into practical use.
Besides, when the conductive foil 52 and the insulating resin layer 53 are laminated, there is a problem that the conductive foil is readily contaminated by powder of the resin which forms the insulating resin layer.
For example, a conventional apparatus for manufacturing a printed wiring board which has the conductive foil 51 and the insulating resin layer 53 laminated has a structure as shown in FIG. 20.
For example, the insulating resin layer 53 such as a prepreg set at a predetermined position is adsorbed by aspiration heads 93 and transported so to be piled on the conductive foil 52 such as a Cu foil set at another predetermined position.
However, such a conventional apparatus has the following disadvantages.
The conventional aspiration heads partly hold the insulating resin layer by a point-to-point contact. Therefore, there is a problem that the insulating resin layer has a wrinkle when it is held and the resin forming-the insulating resin layer is partly powdered to disperse to the surroundings. Furthermore, the powdered and dispersed portion of the insulating resin such as a prepreg adheres to the surface of the conductive foil and the like. As a result, an etching failure is caused or a dent is formed due to irregularities formed by the resin adhered after pressing.
In addition, the powdered prepreg produced in a step of cutting the prepreg adheres to the surface and end faces of the prepreg, and the powder has a problem of causing the same disadvantages as described above.